Re: RADSAFE: Chart of Nuclides Question - black square

[Rick_Strickert@radian.com (Rick Strickert)]

Luke McCormick asked about the black squares (e.g., for Eu-154,
Pm-150, and Cs-136) in the GE Chart of the Nuclides.

According to the 14th Edition of the GE Chart (booklet form, p.10),
shielded nuclides with independent fission yields greater than 2.5E-6%
are indicated by a black square in the lower right hand corner.

Another shielded nuclide with a black square is Sb-124, a fission
product that has the stable Sn-124 blocking beta decay contributions
from earlier (lower Z) members in the primary fission chain for that
mass.

The fission fragment charge dispersion for a given mass in low-energy
fission process (e.g. th.n.f. of U-235) can be described by a gaussian
distribution equation centered around Zp, the most probable charge (not
necessarily integral).  This was described in a number of papers by
Arthur C. Wahl and co-workers in the early 60's.  Later an odd-even
effect was also observed in which even-Z nuclides in the mass chain had
slightly higher independent yields and adjacent odd-Z nuclides slightly
lower yields than the fitted gaussian curve predictions for a given
mass chain.

So, if the shielded nuclide has in a mass that has a significant fission
yield AND a nuclear charge close enough to Zp, it will have a suffiently
high ind. fission yield to get a black square in the lower right hand
corner.  There are shielded nuclides that do not.

Rick

|~~~~\  /~\  |~~~~\ |~|  /~\  |~\_|~||~~~~~| Richard G. Strickert, Ph.D.
| [> / / _ \ |  D  || | / _ \ | \ \ ||     | POBox 201088, Austin, TX 78720
|_||_\/_| |_\|____/ |_|/_| |_\|_|\__||     | (512)310-5259  FAX (512)244-0160
-------------------------------------| LLC | Internet:Rick_Strickert@radian.com
I  N  T  E  R  N  A  T  I  O  N  A  L|_____|   ---> "All written IMHO." <---